Field of the Invention
The invention relates generally to field of exercise performance and nutrition in support thereof. In particular, the invention relates to dietary supplements containing proteins and fats that are readily absorbed, and methods for administering the supplements within a defined period prior to exercise.
Description of Related Art
Performance improvement for canines can be related to increased stamina or endurance while running, tracking, retrieving, swimming, pulling, or any other activity that requires sustained physical movement or exertion during a required task or activity. For dogs, fat metabolism is the primary route for generating energy during sub-maximal exertion. Dogs are inherently “programmed” (evolved) for high endurance activity and metabolism. However, depending on the level of exercise conditioning, physical fitness, and frequency of exercise, fatigue will occur. Hence, prolonging endurance and/or performance is of clear benefit, so having an performance enhancing food product or nutrient delivery system would be advantageous.
In dogs, fat oxidation provides most of the animal's energy at low rates of energy expenditure, whereas with humans, energy is more preferentially generated from glucose from glycogen stores. More specifically, for dogs, the amount of energy from fat oxidation at rest and during exercise is twice that in less aerobic species such as goats (McLelland et al., 1994, Am. J. Physiol. 266 (4 Pt. 2): R1280-1286; Weibel et al., 1996, J. Exp. Biol. 199 (8): 1699-1709). In humans, carbohydrate oxidation supports the intermediate speed of marathon runners until all glycogen stores have been depleted, whereupon fat oxidation becomes the only source available for energy (Hultman et al., 1994, in Modern Nutrition in Health and Disease, M. E. Shils, J. A. Olson, and M. Shike, eds; Lea & Febiger, Philadelphia, pp. 663-685). Consequently, stamina for humans is limited by the amount of glycogen in muscle, whereas in dogs, activation of fat metabolism and conversion of amino acids into glucose becomes initiated soon after exercise, thus contributing to an overall increased aerobic capacity and endurance.
Muscle fiber variation among different animals also contributes to the degree in which either aerobic or anaerobic sources of energy are used. In dogs and cats, muscles contain different muscle fiber types. Specifically, all fiber types in dogs have high aerobic capacity, thus are fatigue resistant. In contrast, the muscle fibers of cats can be divided into low aerobic type that relies on anaerobic metabolism, or a high aerobic type with high capacity for aerobic metabolism. Consequently, maximum oxygen metabolism capacity (VO2max) and blood flow at VO2max in leg (gastrocnemius) muscles have been determined to be about five times higher in dogs than cats. Thus, dogs are adapted for endurance exercise using fat as an energy source, whereas cats are adapted for short bursts of activity such as that required when jumping and pouncing on prey, thus using glycogen as the energy source.
Exercise performance for canines is also significantly related to protein and amino acid metabolism. Protein and amino acid synthesis and catabolism increase in exercising dogs. Synthesis increases to accommodate the changes associated with training and to replace protein and amino acids catabolized during exercise. Protein and amino acids are catabolized during exercise as a source of energy, particularly within exercising muscles, and as precursors of gluconeogenesis. Gluconeogenesis plays an important role in exercise, particularly in exercise lasting longer than 30 minutes, as gluconeogenic precursors like alanine, lactate, pyruvate and glutamine increase. Importantly, precursors for gluconeogenesis are mobilized from the muscle, gut, and adipose tissue. Glutamine and alanine are important gluconeogenic precursors because they shuttle the ammonia by-product resulting from branched-chain amino acid oxidation out of exercising muscles for conversion to glucose by the liver. Consequently, labile protein sources in the gut appear to be the source of branched-chain amino acids that support exercising muscles and are liberated as a result of exercise-induced muscle protein catabolism.
Physical performance can become altered as a result of cell stress and cellular damage to the muscle. Cellular damage is a natural consequence of exercise, and results from excessive protein catabolism, as well as oxidative stress occurring from free-radicals generated by aerobic respiration. The term “cellular damage” is well established within the sport/exercise research community. The degree to which this metabolic condition occurs is related to several factors, including conditioning, duration, intensity, and recurrence of exercise, as well as to nutrition, which can be used to alter this metabolic condition in a favorable manner.
Following exercise-induced muscle damage there is a reduction in the ability of the muscle to contract with maximal force (Pearce et al., 1998, J. Sci. Med. Sport 1: 236-244), which is observed in all three types of muscle action; eccentric (lowering of lifted weight or lengthening of muscle), concentric (lifting weight or shortening of muscle), and isometric (muscle length does not change during contraction) (Turner et al., 2008, J. Appl. Physiol. 105: 502-509), as well as jumping (Kirby et al., 2012, Amino Acids 42(5): 1987-1996).
The depletion of intracellular branched-chain amino acid levels in muscle cells during exercise results from their oxidation as an energy source. Intracellular depletion of branched-chain amino acids, particularly leucine, also corresponds to a reduction in circulating plasma concentrations. Doses of BCAAs (0.050 to 0.100 g/kg BW) ingested before endurance and resistance exercise reduced muscle damage biomarkers (i.e., CK), muscle soreness during recovery (DOMS: delayed onset of muscle soreness) and reduced muscle fatigue (Greer et al., 2007, Int. J. Sport Nutr. Exerc. Metab. 17(6): 595-607; Jackman et al., 2010, Med. Sci. sports Exerc. 42(5): 962-70).
Currently, there is no effective food for animals, particularly for dogs, that can be fed before exercise that can adequately prime their metabolism or minimize endogenous protein breakdown to enhance their endurance and/or reduce the natural catabolic state induced by exercise, and subsequently improve their performance during an exercise bout. Furthermore, reducing the extent of the exercise-induced catabolic state will hasten post-exercise recovery. For example, within the dog performance snack market, current products are formulated with high levels of carbohydrates and very little fat—likely below 6%. This would lead to an elevation in insulin secretion, which would result in a reduction in the activity of exercise-related metabolic pathways. Typically, these products also are low in protein (e.g., below 10%) and the protein sources they contain are not formulated for ready digestion.